Positive and negative sequence PR modular multi-level matrix type converter circulation control method and device, electronic equipment and medium

Abstract

The invention belongs to the field of direct current transmission system control, and particularly relates to a positive and negative sequence PR modular multi-level matrix type converter circulation control method and a medium. The method comprises the following steps: decoupling a circulating current component from industrial frequency transformer valve side current, low frequency transformer valve side current and bridge arm current of the modular multilevel matrix converter (M3C); according to the phase sequence characteristics of the three-phase bridge arm current frequency, analyzing the current frequency phase sequence characteristics of a circulation component carried in the bridge arm current; according to the current frequency phase sequence characteristics of the circulation component, the circulation component current frequency is obtained, wherein the circulation component current frequency forms a non-single frequency doubled circulation frequency by a power frequency () and a low frequency (); and performing Park change with the sum as a rotation angle on the three-phase bridge arm current, respectively adjusting the three-phase bridge arm current by a PR controller with the sum as a resonant frequency, synthesizing a bridge arm circulating current component through a modulation coefficient and reverse Park change, and continuously iterating to eliminate the circulating current frequency. Therefore, the circulation component in the M3C is inhibited, and the problem of instability in the M3C is solved.

Description

Technical Field

[0001] This invention belongs to the field of DC transmission system control, specifically relating to a positive and negative sequence PR modular multilevel matrix converter circulating current control method and medium. Background Technology

[0002] Offshore wind power grid connection faces numerous technical challenges, especially the efficiency and stability of the transmission system. The M3C (Modular Multilevel Matrix Converter), a novel type of power electronic converter, offers unique advantages in frequency division transmission technology. By reducing the transmission frequency, it can significantly increase the transmission capacity of the line, making it particularly suitable for long-distance, high-capacity offshore wind power transmission.

[0003] In the M3C transmission system, there are circulating current components (also known as "steady-state circulating harmonic components") in each bridge arm. These circulating current components not only affect the power quality of the system, but may also cause the system to be unstable. Summary of the Invention

[0004] The purpose of this invention is to provide a circulating current control method, device, electronic device, and medium for a positive-negative sequence PR (Proportion Resonant Controller) modular multilevel matrix converter, in order to solve the instability problem of modular multilevel matrix converters in existing offshore wind power grid-connected scenarios.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a circulating current control method for a positive-negative sequence PR modular multilevel matrix converter, comprising: Decouple the circulating current component from the valve-side current of the M3C power frequency transformer, the valve-side current of the low frequency transformer, and the bridge arm current. The phase sequence characteristics of the current frequency carrying the circulating current component in the bridge arm current are analyzed based on the phase sequence characteristics of the three-phase bridge arm current frequency. The current frequency of the circulating current component is obtained based on the phase sequence characteristics of the current frequency of the circulating current component. The current frequency of the circulating current component is a non-single frequency doubling of the circulating current frequency composed of the power frequency and the low frequency. After the three-phase bridge arm current is varied by Park with a rotation angle of low frequency and twice the low frequency, it is adjusted by PR controller with a resonant frequency of power frequency and twice the power frequency, and then the bridge arm circulating current component is synthesized by modulation coefficient and inverse Park variation to continuously eliminate the circulating current frequency.

[0006] Furthermore, after the three-phase bridge arm current is subjected to Park changes with rotation angles at low frequency and twice the low frequency, and then adjusted by PR controllers with resonant frequencies at the power frequency and twice the power frequency respectively, the bridge arm circulating current component is synthesized after modulation coefficient and inverse Park changes, and the circulating current frequency is iteratively eliminated, including: The three-phase bridge arm current is first changed by Park and then passes through the PR controller, which has a resonant bandwidth of twice the power frequency, and then passes through the modulation coefficient. and synchronous rotating reference angle at low frequency The first inverse Park transform yields the first circulating modulated signal component. The first Park change uses a low-frequency frequency as the synchronous rotation reference angle. The three-phase bridge arm current is transformed by a second Park change and then passed through a PR controller, which uses the power frequency as its resonant bandwidth, and then passed through a modulation coefficient... and a synchronous rotating reference angle at twice the low frequency The second inverse Park transform yields the second circulating modulated signal component. The second Park change uses a synchronous rotation parameter at twice the low frequency as the rotation angle. First circulating modulation signal component Second circulating modulation signal component The combined components are the bridge arm circulation components.

[0007] Furthermore, the three-phase bridge arm current, after undergoing the first Park change, passes through a PR controller, which uses twice the power frequency as its resonant bandwidth, and then passes through a modulation coefficient... and synchronous rotating reference angle at low frequency The first inverse Park transform yields the first circulating modulated signal component. ,include: The three-phase bridge arm current , and The first d-axis current component and the first q-axis current component are generated by the synchronous rotating reference angle at a low frequency after the first Park change. Obtain the d-axis and q-axis reference values ​​of the bridge arm circulating current, and obtain the difference of the first d-axis circulating current by subtracting the d-axis reference value of the bridge arm circulating current from the first d-axis current component. The difference between the bridge arm circulating current q-axis reference value and the first q-axis current component is used to obtain the difference in the first q-axis circulating current. ; The difference of the first d-axis circulation Difference from the first q-axis circulation As a PR controller The input signal of the PR controller The resonant bandwidth is twice the power frequency, modulated by the coefficient. and synchronous rotating reference angle at low frequency The first inverse Park transform yields the first circulating modulated signal component. .

[0008] Furthermore, the three-phase bridge arm current, after undergoing a second Park change, passes through a PR controller, which uses the power frequency as its resonant bandwidth, and then passes through a modulation coefficient... and synchronous rotating reference angle at low frequency The second inverse Park transform yields the second circulating modulated signal component. ,include: The three-phase bridge arm current , and The second d-axis current component and the second q-axis current component are generated by a synchronous rotating reference angle at twice the low frequency through a second Park change. The difference between the bridge arm circulating current d-axis reference value and the current component of the second d-axis is used to obtain the difference in the second d-axis circulating current. The difference between the bridge arm circulating current q-axis reference value and the second q-axis current component is used to obtain the difference in the second q-axis circulating current. ; The difference between the second d-axis circulation Difference between the second q-axis circulation As a PR controller The input signal, The resonant bandwidth is the power frequency, modulated by the coefficient. and synchronous rotating reference angle at low frequency The second inverse Park transform yields the second circulating modulated signal component. .

[0009] Furthermore, based on the phase sequence characteristics of the three-phase arm current frequencies, the phase sequence characteristics of the current frequencies carrying the circulating current component in the arm currents are analyzed, including: Based on Kirchhoff's current theorem, the relationship between the bridge arm current, the valve-side current of the M3C power frequency transformer, and the valve-side current of the low frequency transformer is obtained, and the time-domain expression of the bridge arm capacitor voltage is obtained. The time-domain expression of the bridge arm voltage is obtained from the time-domain expression of the bridge arm capacitor voltage; Expanding the time-domain expression of the bridge arm voltage yields the phase sequence characteristics of the bridge arm capacitor voltage frequency and the bridge arm current frequency. The phase sequence characteristics of the bridge arm current frequency are obtained, and the phase sequence characteristics of the bridge arm current frequency are subjected to modulus calculation. The current component with the value of the modulus calculation is extracted to obtain the current frequency phase sequence characteristics of the circulating current component.

[0010] Furthermore, the specific steps for decoupling the circulating current component from the valve-side current of the M3C power frequency transformer, the valve-side current of the low-frequency transformer, and the arm current include: Based on Kirchhoff's current law, the relationship between the valve-side current of the M3C power frequency transformer, the valve-side current of the low frequency transformer, and the bridge arm current is obtained. Based on the relationship between the valve-side current of the M3C power frequency transformer, the valve-side current of the low frequency transformer, and the bridge arm current, the time-domain expressions of the M3C power frequency loop, the low frequency loop, and the circulating current loop are obtained. The time-domain expression of the circulating current loop includes the circulating current component, the M3C power frequency component, and the low frequency component. The time-domain expression of the circulating loop is decoupled to obtain the circulating component.

[0011] Furthermore, the specific steps for decoupling the time-domain expression of the circulating loop to obtain the circulating components include: Calculate the differential mode voltage of the M3C bridge arm. :

[0012] in, It is the bridge arm voltage. This refers to the common-mode voltage of the M3C power frequency bridge arm. It is the low-frequency bridge arm common-mode voltage; Will Substituting into the time-domain expression of the circulating current loop, where the time-domain expression of the circulating current loop is:

[0013] in, It is the bridge arm resistance. It is the circulating component. , This is the equivalent neutral point voltage; The circulating component is decoupled after transforming the time-domain expression of the circulating loop. .

[0014] Secondly, a positive and negative sequence PR modular multilevel matrix converter circulating current control device is provided, comprising: The decoupling module is used to decouple the circulating current component from the valve-side current of the M3C power frequency transformer, the valve-side current of the low frequency transformer, and the bridge arm current. The analysis module is used to analyze the phase sequence characteristics of the current frequency carrying the circulating current component in the arm current based on the phase sequence characteristics of the three-phase arm current frequency. The acquisition module is used to obtain the current frequency of the circulating current component based on the phase sequence characteristics of the current frequency of the circulating current component; the current frequency of the circulating current component is the circulating frequency that is not a single frequency multiple of the power frequency and the low frequency. The processing module is used to continuously iterate and eliminate the circulating current frequency by performing Park changes on the three-phase bridge arm current with a rotation angle of low frequency and twice the low frequency, then adjusting it with PR controllers with resonant frequencies of power frequency and twice the power frequency, and finally synthesizing the bridge arm circulating current component after modulation coefficient and inverse Park changes.

[0015] Thirdly, the present invention provides an electronic device, including a processor and a memory, wherein the processor is configured to execute a computer program stored in the memory to implement a positive-negative sequence PR modular multilevel matrix converter circulating current control method as described in any one of the preceding claims.

[0016] In a fourth aspect, the present invention provides a computer-readable storage medium storing at least one instruction that, when executed by a processor, implements the above-described positive-negative sequence PR modular multilevel matrix converter circulating current control method.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The method of this invention decouples the circulating current component, which is an interference signal that affects the stability of the modular multilevel matrix converter. Based on the phase sequence characteristics of the three-phase arm current frequencies, the phase sequence characteristics of the current frequency carrying the circulating current component in the arm current are analyzed. The circulating current frequency is obtained from the phase sequence characteristics of the circulating current component, which is a non-single frequency multiple of the power frequency and a low-frequency frequency. The power frequency and low-frequency of the circulating current component are obtained. After Park variation of the three-phase arm current with rotation angles of the low-frequency and twice the low-frequency, the current is adjusted by PR controllers with resonant frequencies of the power frequency and twice the power frequency, respectively. After modulation coefficient and inverse Park variation, the arm circulating current component is synthesized in the modulation signal, and the circulating current frequency is iteratively eliminated. Therefore, the method of this invention can suppress the circulating current component from the circulating current of the modular multilevel matrix converter, thereby improving the stability of the modular multilevel matrix converter. Attached Figure Description

[0018] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a topology diagram of a modular multilevel matrix converter according to an embodiment of the present invention; Figure 2 This is a flowchart of the positive and negative sequence PR modular multilevel matrix converter circulating current control method according to an embodiment of the present invention; Figure 3 This is the time-domain model of the equivalent circuit on the power frequency side of the M3C in this embodiment of the invention; Figure 4 This is the time-domain model of the equivalent loop on the low-frequency side of the M3C in this embodiment of the invention; Figure 5 This is the time-domain model of the internal equivalent loop of M3C in an embodiment of the present invention; Figure 6 This is a schematic diagram of the M3C local average value model in an embodiment of the present invention; Figure 7 This is a diagram of the M3C circulating current control framework according to an embodiment of the present invention; Figure 8 This is a schematic diagram of the M3C power frequency side control structure according to an embodiment of the present invention; Figure 9 This is a schematic diagram of a typical control structure on the low-frequency side of the M3C according to an embodiment of the present invention; Figure 10 The diagram shows the steady-state waveform and FFT result of the bridge arm ua after the circulating current control in the prior art. Among them, (a) is the waveform of the capacitor voltage of the bridge arm ua in the prior art, (b) is the FFT result of the capacitor voltage waveform of the bridge arm ua in the prior art, (c) is the waveform of the current of the bridge arm ua in the prior art, (d) is the FFT result of the current waveform of the bridge arm ua in the prior art, (e) is the waveform of the modulation signal of the bridge arm ua in the prior art, and (f) is the FFT result of the signal waveform of the bridge arm ua in the prior art. Figure 11 The following are schematic diagrams of the steady-state waveform and FFT result of the bridge arm ua after circulating current control in this embodiment of the invention: (a) is a waveform diagram of the capacitor voltage of the bridge arm ua in this embodiment of the invention; (b) is a schematic diagram of the FFT result of the capacitor voltage waveform of the bridge arm ua in this embodiment of the invention; (c) is a waveform diagram of the current waveform of the bridge arm ua in this embodiment of the invention; (d) is a schematic diagram of the FFT result of the current waveform of the bridge arm ua in this embodiment of the invention; (e) is a waveform diagram of the modulation signal of the bridge arm ua in this embodiment of the invention; and (f) is a schematic diagram of the FFT result of the signal waveform of the bridge arm ua in this embodiment of the invention. Figure 12 This is a schematic diagram of the positive and negative sequence PR modular multilevel matrix converter circulating current control device according to an embodiment of the present invention; Figure 13 This is a structural block diagram of a medium and its electronic device according to an embodiment of the present invention. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0020] The following detailed description is exemplary and intended to provide further detailed explanation of the invention. Unless otherwise specified, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terminology used in this invention is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention.

[0021] In M3C transmission systems, circulating current components exist in each bridge arm. These components not only affect the power quality of the system but can also lead to unstable operation. This is especially true in offshore wind power grid-connected scenarios, where the complex environment and maintenance difficulties necessitate even higher requirements for system stability and reliability. Therefore, suppressing steady-state circulating harmonics is a crucial aspect of M3C transmission system design. Existing circulating current component control methods are primarily used in MMC transmission systems. The circulating current components generated by the MMC during operation not only increase the fluctuation of submodule capacitor voltage but also cause additional losses, affecting system efficiency and stability. Due to its unique structure and operating characteristics, the frequency characteristics of M3C circulating harmonic components are more complex than those of MMC circulating harmonic components. Existing strategies for controlling circulating current components in MMCs are difficult to apply directly. Therefore, a circulating current control strategy specifically for modular multilevel matrix converters is urgently needed.

[0022] Existing circulating current control strategies for power transmission system technologies have the following shortcomings: (1) Existing circulating current control strategies (such as proportional-integral (PI) control or proportional-resonant (PR) control) proposed in the literature are mainly aimed at MMC systems, and there is a lack of research on M3C circulating current control. Existing circulating current control strategies are mainly aimed at MMC systems, and their circulating current frequency characteristics are mainly concentrated near the low frequency (100Hz). However, the circulating current harmonics generated by M3C during steady-state operation are not only related to the power frequency (50Hz) but also to the low frequency (20Hz), resulting in a significant difference between the circulating current characteristics of M3C and MMC. The circulating current frequency characteristics are more complex. Existing control strategies lack in-depth research on the circulating current frequency characteristics of M3C, cannot be directly applied to M3C systems, and are difficult to accurately identify and suppress the circulating current components in M3C, resulting in difficulties in circulating current control design and poor suppression effect.

[0023] (2) In the M3C system, there is a strong coupling relationship between the power frequency, low frequency and circulating current loops. This coupling makes it difficult to control each electrical parameter independently. Existing control strategies have failed to effectively solve the coupling problem between M3C electrical parameters, resulting in insufficient control accuracy, affecting system stability, and making it difficult to achieve precise control design of M3C electrical parameters.

[0024] Therefore, in order to solve the above-mentioned technical problems, this invention proposes a circulating current control method for a positive and negative sequence modular multilevel matrix converter, thereby suppressing the circulating current component in the modular multilevel matrix converter and making the modular multilevel matrix converter of this invention more stable.

[0025] Example 1 Figure 1 This is a topology diagram of a modular multilevel matrix converter according to an embodiment of the present invention. The valve side of the M3C power frequency transformer and the valve side of the low frequency transformer are connected by nine bridge arms, each bridge arm consisting of N SMs and a bridge arm inductor. Bridge arm resistance It is connected in series.

[0026] and These represent the three-phase AC voltage and current on the valve side of the M3C power frequency transformer. They represent , , Mutually.

[0027] and These represent the three-phase AC voltage and current on the valve side of the M3C low-frequency transformer. They represent , , Mutually.

[0028] and Connecting to power frequency Phase and low frequency The phase arm voltage and the phase arm current.

[0029] Each arm of the M3C bridge is composed of multiple identical sub-modules with a full-bridge structure connected in series. This represents the capacitor voltage of the submodule.

[0030] Figure 2 This is a flowchart of the circulating current control method for a positive and negative sequence PR modular multilevel matrix converter according to an embodiment of the present invention. The method of the present invention includes steps 100-400.

[0031] Step 100: Decouple the circulating current component from the valve-side current of the M3C power frequency transformer, the valve-side current of the low frequency transformer, and the bridge arm current. Step 200: Based on the phase sequence characteristics of the three-phase bridge arm current frequency, analyze the phase sequence characteristics of the current frequency carrying the circulating current component in the bridge arm current. Step 300: Obtain the current frequency of the circulating current component based on the phase sequence characteristics of the current frequency of the circulating current component. The current frequency of the circulating current component is the circulating frequency that is a non-single frequency multiple of the power frequency and the low frequency. Step 400: After the three-phase bridge arm current is changed by Park with a rotation angle of low frequency and twice the low frequency, it is adjusted by PR controller with a resonant frequency of power frequency and twice the power frequency, and then the bridge arm circulating current component is synthesized by modulation coefficient and inverse Park change to continuously eliminate the circulating current frequency.

[0032] The method of this invention decouples the circulating current component, which is an interference signal affecting the stability of the modular multilevel matrix converter. Based on the phase sequence characteristics of the three-phase arm current frequencies, the phase sequence characteristics of the current frequency carrying the circulating current component in the arm current are analyzed. The circulating current component frequency is obtained from the phase sequence characteristics of the circulating current component, which is a non-single frequency multiple of the power frequency and a low-frequency frequency. The relationship between the circulating current component frequency and the power frequency and low-frequency frequency is obtained. After Park variation of the three-phase arm current with rotation angles of the low-frequency and twice the low-frequency frequency, and adjustment by PR controllers with resonant frequencies of the power frequency and twice the power frequency respectively, and then iteratively eliminating the circulating current frequency by synthesizing the arm circulating current component in the modulation signal after modulation coefficient and inverse Park variation, the method of this invention can suppress the circulating current component from the circulating current of the modular multilevel matrix converter, thereby improving the stability of the modular multilevel matrix converter.

[0033] Step 100 is described in detail below.

[0034] Step 100: Decouple the circulating current component from the valve-side current of the M3C power frequency transformer, the valve-side current of the low frequency transformer, and the bridge arm current.

[0035] Step 100 is a method for decoupling the circulating current component provided by an embodiment of the present invention. Addressing the challenge of control strategy design caused by the coupling between electrical parameters in a modular multilevel matrix converter (MMC), this invention derives equivalent models for the power frequency, low frequency, and circulating current loops by using the bridge arm loop equations and combining them with the three-phase symmetry characteristics of the MMC during steady-state operation. This achieves decoupled control of the power frequency, low frequency, and circulating current, reducing the mutual influence between control loops, thereby improving the system's control accuracy and stability, and providing a theoretical basis for subsequent decoupled control.

[0036] Figure 3 This is the time-domain model of the M3C power frequency side equivalent circuit in an embodiment of the present invention.

[0037] Figure 4 This is the time-domain model of the equivalent loop on the low-frequency side of the M3C in this embodiment of the invention.

[0038] Figure 5 This is the time-domain model of the internal equivalent loop of M3C in an embodiment of the present invention.

[0039] Reference Figure 3 , Figure 4 and Figure 5 In some embodiments of the present invention, step 100 includes three sub-steps: step 110 to step 130.

[0040] Step 110: According to Kirchhoff's current law, obtain the relationship between the valve-side current of the M3C power frequency transformer, the valve-side current of the low frequency transformer, and the bridge arm current. Step 120: Based on the relationship between the valve-side current of the M3C power frequency transformer, the valve-side current of the low frequency transformer, and the bridge arm current, obtain the relationship between the bridge arm current and the valve-side current of the M3C power frequency transformer and the valve-side current of the low frequency transformer, as well as the relationship between the three-phase AC current and the three-phase AC voltage of the M3C power frequency side and the valve side of the low frequency transformer, and obtain the time-domain expression of the M3C power frequency loop, the time-domain expression of the low frequency transformer loop, and the time-domain expression of the circulating current loop. The time-domain expression of the circulating current loop includes the circulating current component, the M3C power frequency component, and the low frequency transformer component. Step 130: Decouple the circulating components to obtain the time-domain model of the circulating loop.

[0041] In some embodiments of the present invention, the time-domain expression of the circulating loop is as follows: (1) in, It is the bridge arm resistance. It is a bridge arm inductor. It is the circulating current component. This refers to the common-mode voltage of the three-phase power frequency bridge arm. The equivalent neutral point voltage, This refers to the differential mode voltage of the M3C bridge arm.

[0042] In some embodiments of the present invention, the differential mode voltage of the M3C bridge arm... The expression is: (2) in, It is the bridge arm voltage. This refers to the common-mode voltage of the M3C power frequency bridge arm. It is the common-mode voltage of the low-frequency bridge arm.

[0043] In some embodiments of the present invention, the methods for obtaining the power frequency bridge arm common-mode voltage and the low frequency bridge arm common-mode voltage are as follows: The common-mode voltage of the power frequency bridge arm is obtained by the time-domain expression of the M3C power frequency loop. The common-mode voltage of the low-frequency bridge arm is obtained by expressing the time-domain characteristics of the low-frequency transformer circuit.

[0044] Based on the three-phase symmetry during steady-state operation, decoupling of the power frequency, low frequency, and circulating current loops is achieved. During steady-state operation of the M3C, the three-phase voltages and currents on the valve side of the power frequency transformer, the three-phase voltages and currents on the valve side of the low-frequency transformer all satisfy three-phase symmetry, i.e., they satisfy the following expression: (3) The bridge arm circulation satisfies the following expression: (4) According to KCL, the relationship between the three-phase current on the valve side of the power frequency transformer, the three-phase current on the valve side of the low frequency transformer, and the bridge arm current can be obtained as follows: (5) The relationship between the bridge arm current and the valve side current of the power frequency and low frequency transformers is as follows: (6) The relationship between the three-phase AC current and three-phase AC voltage on both sides of the M3C power frequency and low frequency transformers can be expressed as follows: (7) (8) In the formula: and These are the turns ratios of the M3C high-frequency transformer and the low-frequency transformer, respectively.

[0045] In this embodiment of the invention, based on Kirchhoff's current law, the relationship between the valve-side current of the M3C power frequency transformer, the valve-side current of the low-frequency transformer, and the bridge arm current is obtained. Based on this relationship, the relationship between the bridge arm current and the valve-side currents of the M3C power frequency transformer and the low-frequency transformer is also obtained. Furthermore, the relationship between the three-phase AC current and three-phase AC voltage on the M3C power frequency side and the valve side of the low-frequency transformer is obtained. Time-domain expressions for the M3C power frequency loop, the low-frequency transformer loop, and the circulating current loop are then obtained. This decouples the circulating current loop, achieving decoupling between the M3C power frequency side, the low-frequency transformer valve side, and the circulating current loop. This reduces the mutual influence between the various control loops, thereby improving the control accuracy and stability of the system.

[0046] Step 200: Based on the phase sequence characteristics of the three-phase bridge arm current frequency, analyze the phase sequence characteristics of the current frequency carrying the circulating current component in the bridge arm current. Step 200 includes four sub-steps, steps 210-240.

[0047] Step 210: According to Kirchhoff's current theorem, obtain the relationship between the bridge arm current, the valve side current of the M3C power frequency transformer and the valve side current of the low frequency transformer, and obtain the time-domain expression of the bridge arm capacitor voltage. Step 220: Obtain the time-domain expression of the bridge arm voltage based on the time-domain expression of the bridge arm capacitor voltage; Step 230: Expand the time-domain expression of the bridge arm voltage to obtain the phase sequence characteristics of the bridge arm capacitor voltage frequency and the bridge arm current frequency; Step 240: After performing modulus calculation on the phase sequence characteristics of the bridge arm current frequency, the value is taken as... The phase sequence characteristics of the current frequency of the circulating current component are obtained by extracting the current component.

[0048] M3C ensures capacitor voltage balancing between submodules during operation. Therefore, the detailed M3C model can be transformed into, for example: Figure 3 The average value model shown is for ease of analysis and modeling.

[0049] The relationship between bridge arm voltage, bridge arm current, and capacitor voltage can be expressed as: (9) (10) Figure 6 This is a schematic diagram of the M3C local average value model in an embodiment of the present invention.

[0050] Reference Figure 6 Based on the M3C local average value model, considering the inductance of the bridge arm and the voltage drop across the resistor, the relationship between the bridge arm voltage, the valve-side voltage of the power frequency transformer, and the valve-side voltage of the low-frequency transformer can be expressed as follows: (11) (12) (13) in: (14) In the formula, To convert the voltage between the power frequency AC neutral point and the low frequency AC neutral point on the transformer valve side, and These are the voltages of the power frequency AC neutral point and the low frequency AC neutral point, respectively.

[0051] Obtain the voltage, current frequency, and phase sequence characteristics of the bridge arm capacitors; The resistance and reactance of the bridge arm do not affect the frequency distribution characteristics of the bridge arm voltage. To obtain the frequency and phase sequence characteristics of the bridge arm capacitor voltage and current, one can... Figure 2 Neglecting the resistance and inductance of the bridge arms in the M3C average value model, the bridge arm voltage can be derived as follows: (15) In the formula, , These represent the amplitude and phase of the fundamental frequency component of the valve-side voltage of the M3C power frequency transformer, respectively. , These represent the amplitude and phase of the fundamental frequency component of the valve-side voltage of the M3C low-frequency transformer, respectively. and This is the phase shift angle for the three phases.

[0052] When the M3C is running stably, the bridge arm equivalent capacitor voltage is running stably at... Nearby, simplifying equation (15), the bridge arm modulation signal can be obtained as: (16) in (17) Based on Kirchhoff's current theorem, the relationship between the bridge arm current and the three-phase AC current on the valve side of the M3C power frequency and low frequency transformers can be derived as follows: (18) (19) Substituting (8) and (11) into (1), we can obtain the time-domain expression for the bridge arm capacitor voltage as follows: (20) The time-domain expression for the bridge arm voltage is:

[0053] The frequency distribution characteristics of the system bridge arm capacitor voltage and current shown in Table 1 can be obtained through the above time-domain expansion: (twenty two) (twenty three) Based on formulas (22) and (23), the frequency distribution characteristics of the bridge arm capacitor voltage, bridge arm voltage, bridge arm current, and modulation signal are summarized, as shown in Table 1:

[0054] Table 1 Based on formulas (22) and (23), the frequency composition of the power frequency, low frequency, and bridge arm electrical parameters is summarized, as shown in Table 2:

[0055] Table 2 In this embodiment of the invention, the phase sequence characteristics of the circulating current component in the three-phase bridge arm current are obtained through steps 210-240. Please refer to Tables 1 and 2 to obtain the steady-state harmonic frequencies of the three-phase bridge arm current through steps 210-240. middle ( Interphase sequence for ,as well as ( Interphase sequence for The components constitute the phase sequence characteristics of the circulating current frequency.

[0056] See Table 2 for the modulus calculation process. The phase sequence characteristic is the power frequency side current frequency, which is used in the modulus calculation process. The phase sequence characteristic is the frequency of the low-frequency side current, which is used in the modulus calculation process. as well as The phase sequence characteristic is the current frequency characteristic of the circulating current component.

[0057] Step 300: Obtain the current frequency of the circulating current component based on the phase sequence characteristics of the current frequency of the circulating current component. The current frequency of the circulating current component is a non-single frequency multiple of the circulating current frequency composed of the power frequency and the low frequency. First, obtain the phase sequence characteristics of the current frequency of the circulating current component obtained in step 200; second, resolve the phase sequence characteristics of the current frequency of the circulating current component into the current frequency of the circulating current component.

[0058] Please refer to Table 1, since the frequency of the bridge arm current is... ,in, It is the power frequency. It is a low-frequency frequency. After the modulus calculation in step 200, as well as The phase sequence characteristics are the current frequency characteristics of the circulating current component. Therefore, the circulating current frequency obtained in step 300 is determined by... , , , These circulating frequencies, which are composed of power frequency and low-frequency frequencies and are not single-frequency multipliers, are unstable and interfere with the modular multilevel matrix converter. Therefore, in the subsequent step 400, it is necessary to suppress these frequencies (circulating frequencies composed of power frequency and low-frequency frequencies and are not single-frequency multipliers).

[0059] Figure 7 This is a diagram of the M3C circulating flow control framework according to an embodiment of the present invention.

[0060] Please refer to Figure 7 .

[0061] The present invention removes the circulating current component in the modular multilevel matrix converter according to step 400.

[0062] Step 400: After the three-phase bridge arm current is changed by Park with a rotation angle of low frequency and twice the low frequency, it is adjusted by PR controller with a resonant frequency of power frequency and twice the power frequency, and then the bridge arm circulating current component is synthesized by modulation coefficient and inverse Park change to continuously eliminate the circulating current frequency.

[0063] In some embodiments of the present invention, step 400 includes three sub-steps: step 410-step 430.

[0064] Step 410: After the three-phase bridge arm current undergoes the first Park change, it passes through the PR controller, which uses twice the power frequency as its resonant bandwidth, and then passes through the modulation coefficient... and synchronous rotating reference angle at low frequency The first inverse Park transform yields the first circulating modulated signal component. ; Step 420: The three-phase bridge arm current is transformed by the second Park change and then passed to the PR controller. The PR controller uses the power frequency as the resonant bandwidth and then passes through the modulation coefficient. and a synchronous rotating reference angle at twice the low frequency The second inverse Park transform yields the second circulating modulated signal component. ; Step 430, First circulating current modulation signal component Second circulating modulation signal component The components are added together to synthesize the bridge arm circulating current component. Specifically, the first circulating current modulation signal component... Second circulating modulation signal component The bridge arm circulating current component is obtained by adding the restored power frequency modulation signal and the restored low frequency modulation signal after removing the circulating current component. Bridge arm circulation component middle , , , The frequency is suppressed, and the bridge arm circulation component Only includes frequencies of , The amount.

[0065] Step 410 includes three sub-steps: Step 411-Step 413.

[0066] Step 411, convert the three-phase bridge arm current , and The first d-axis current component and the first q-axis current component are generated by the synchronous rotating reference angle at the power frequency after the first Park change. Step 412: Obtain the d-axis and q-axis reference values ​​of the bridge arm circulating current (0), and obtain the difference between the bridge arm circulating current d-axis reference value and the first d-axis current component. The difference between the bridge arm circulating current q-axis reference value and the first q-axis current component is used to obtain the difference in the first q-axis circulating current. The frequency of the circulating current component after iteration of the three-phase bridge arm current. as well as Transformed into the first Park change .

[0067] Step 413, the difference in the first d-axis circulation Difference from the first q-axis circulation As a PR controller The input signal of the PR controller The resonant bandwidth is twice the power frequency, modulated by the coefficient. and synchronous rotating reference angle at low frequency The first inverse Park transform yields the first circulating modulated signal component. .

[0068] Step 420 includes three sub-steps: Step 421-Step 423.

[0069] Step 421, the three-phase bridge arm current , and The second d-axis current component and the second q-axis current component are generated by a synchronous rotating reference angle at twice the low frequency through a second Park change. Step 422: Obtain the difference of the second d-axis circulating current by the difference between the bridge arm circulating current d-axis reference value and the current component of the second d-axis. The difference between the bridge arm circulating current q-axis reference value and the second q-axis current component is used to obtain the difference in the second q-axis circulating current. The current frequency of the circulating current component after iteration of the three-phase bridge arm current. as well as Transformed into the second Park change .

[0070] Step 423, the difference in the second d-axis circulation Difference between the second q-axis circulation As a PR controller The input signal, The resonant bandwidth is the power frequency, modulated by the coefficient. and a synchronous rotating reference angle at twice the low frequency The second inverse Park transform yields the second circulating modulated signal component. .

[0071] Bridge arm current by To synchronously rotate the reference angle, d-axis and q-axis current components are generated after Park's transformation. , That is, the current frequency of the circulating current component after the first Park change. as well as Convert to .

[0072] Bridge arm current by To synchronously rotate the reference angle, d-axis and q-axis current components are generated after Park's transformation. , That is, after the second Park change, the current frequency of the circulating current component... as well as Convert to .

[0073] in, It is a low-frequency synchronous rotation reference angle. It is a synchronous rotation reference angle at twice the low frequency.

[0074] The reference values ​​for the d-axis and q-axis of the bridge arm circulation are both 0. The reference values ​​for the d-axis and q-axis of the bridge arm circulation are... , The difference, as a PR control The input signal, The resonant bandwidth is twice the power frequency. (100Hz), modulated by coefficient and To obtain the circulating modulation signal component by the inverse Park transform of the synchronous rotating reference angle. ; Bridge arm circulation d and q axis reference values ​​and , The difference, as a PR control The input signal, The resonant bandwidth is the power frequency. (50Hz), modulated by coefficient and To obtain the circulating modulation signal component by the inverse Park transform of the synchronous rotating reference angle. Circulating modulation signal components and The addition generates the bridge arm circulating current component of the M3C modulated signal. The M3C circulating component is suppressed by positive and negative order Park transformation, PR control, and inverse Park transformation.

[0075] Refer to Table 3, which shows the phase sequence of the circulating current components (steady-state harmonics) in the first iteration. The PR controller can precisely control the problematic harmonics of the circulating current components at specific frequencies. Therefore, based on the steady-state harmonic phase sequence of the circulating current components in the first iteration, the M3C circulating current control method based on positive and negative sequence PR control of this invention is proposed.

[0076]

[0077] Table 3 Specifically, the present invention, by performing Park changes on the three-phase bridge arm currents with rotation angles of low frequency and twice the low frequency, and then adjusting them respectively by PR controllers with resonant frequencies of power frequency and twice the power frequency, and further iterating and eliminating the circulating current frequency by modulating the modulation coefficient and inverse Park changes, can synthesize the bridge arm circulating current component. This improves the stability of the multilevel matrix converter of the present invention.

[0078] The method of this invention decouples the circulating current component, which is an interference signal that affects the stability of the modular multilevel matrix converter. Based on the phase sequence characteristics of the three-phase arm current frequencies, the phase sequence characteristics of the current frequency carrying the circulating current component in the arm current are analyzed. The circulating current frequency is obtained from the phase sequence characteristics of the circulating current component, which is a non-single frequency multiple of the power frequency and a low-frequency frequency. The power frequency and low-frequency of the circulating current component are obtained. After Park variation of the three-phase arm current with rotation angles of the low-frequency and twice the low-frequency, the current is adjusted by PR controllers with resonant frequencies of the power frequency and twice the power frequency, respectively. After modulation coefficient and inverse Park variation, the arm circulating current component is synthesized in the modulation signal, and the circulating current frequency is iteratively eliminated. Therefore, the method of this invention can suppress the circulating current component from the circulating current of the modular multilevel matrix converter, thereby improving the stability of the modular multilevel matrix converter.

[0079] Figure 8 This is a schematic diagram of the M3C power frequency side control structure according to an embodiment of the present invention; Figure 9 This is a schematic diagram of a typical control structure on the low-frequency side of the M3C according to an embodiment of the present invention; Figure 10The diagram shows the steady-state waveform and FFT result of the bridge arm ua after the circulating current control in the prior art. Among them, (a) is the waveform of the capacitor voltage of the bridge arm ua in the prior art, (b) is the FFT result of the capacitor voltage waveform of the bridge arm ua in the prior art, (c) is the waveform of the current of the bridge arm ua in the prior art, (d) is the FFT result of the current waveform of the bridge arm ua in the prior art, (e) is the waveform of the modulation signal of the bridge arm ua in the prior art, and (f) is the FFT result of the signal waveform of the bridge arm ua in the prior art. Figure 11 The following are schematic diagrams of the steady-state waveform and FFT result of the bridge arm ua after circulating current control in this embodiment of the invention: (a) is a waveform diagram of the capacitor voltage of the bridge arm ua in this embodiment of the invention; (b) is a schematic diagram of the FFT result of the capacitor voltage waveform of the bridge arm ua in this embodiment of the invention; (c) is a waveform diagram of the current waveform of the bridge arm ua in this embodiment of the invention; (d) is a schematic diagram of the FFT result of the current waveform of the bridge arm ua in this embodiment of the invention; (e) is a waveform diagram of the modulation signal of the bridge arm ua in this embodiment of the invention; and (f) is a schematic diagram of the FFT result of the signal waveform of the bridge arm ua in this embodiment of the invention. The following is a verification process of the positive and negative sequence PR modular multilevel matrix converter circulating current control method according to an embodiment of the present invention. Please refer to... Figures 8-11 .

[0080] In one specific embodiment, the main circuit and control parameters of the modular multilevel matrix converter of the present invention are shown in Table 4:

[0081] Table 4 According to the positive and negative sequence PR modular multilevel matrix converter circulating current control method provided in steps 100-400 of the present invention, refer to Figure 8 and Figure 9 In network mode, the PLL controls and tracks the phase of the three-phase AC grid voltage on the power frequency side, and the bridge arm current is... To synchronize the rotation reference angle, the d, q, and 0 axis components are obtained after Park transformation. The outer loop uses bridge arm capacitor voltage control, and the inner loop uses AC current control, modulated by the coefficient. And the three-phase power frequency component of the M3C modulated signal generated by the inverse Park transform. The M3C low-frequency side adopts islanded mode, and in islanded output mode, there is no PLL control. The zero-axis current is generated after the bridge arm current is varied by the power frequency Park. , , This constitutes the low-frequency component of the bridge arm current, and then... To synchronize the rotation of the reference angle, the d- and q-axis components of the bridge arm current on the low-frequency side are obtained after Park transformation. , The low-frequency AC voltage control outer loop is implemented in a synchronous rotating coordinate system, while the inner loop uses three-phase AC current control, modulated by a modulation coefficient. And the three-phase low-frequency components of the M3C modulated signal generated by the inverse Park transform. The accuracy of the derived equivalent models for power frequency, low frequency, and circulating current loops was verified, and control decoupling was achieved.

[0082] Reference Figure 10 Under steady-state operation, the M3C bridge arm current, capacitor voltage, and modulation signal contain abundant harmonic components, with DC, power frequency, and low-frequency components being the main components. The bridge arm current contains components with frequencies of... , , , The circulating component, the bridge arm modulation signal contains only as well as The steady-state frequency components.

[0083] Reference Figure 11 The circulation frequency after one iteration is , , , The secondary and subsequent iterations of the circulating current components are obtained through the interaction of the primary iteration's steady-state harmonic components and the modulation signal. Therefore, the primary circulation steady-state harmonic components can be suppressed. In addition to the bridge arm modulation signal... as well as In addition to frequency components, it also includes , , , The component of the bridge arm circulation component middle , , , The frequency is suppressed, and only the frequency of is included. , The components were analyzed. This verified the effectiveness of the circulating current control of the positive and negative sequence PR modular multilevel matrix converter according to the present invention.

[0084] Figure 12 This is a schematic diagram of the positive and negative sequence PR modular multilevel matrix converter circulating current control device according to an embodiment of the present invention.

[0085] Reference Figure 12 The present invention also provides a positive and negative sequence PR modular multilevel matrix converter circulating current control device, comprising: a decoupling module, a decoupling module, an acquisition module, and a processing module.

[0086] The decoupling module is used to decouple the circulating current component from the valve-side current of the M3C power frequency transformer, the valve-side current of the low frequency transformer, and the bridge arm current. The decoupling module is used to analyze the phase sequence characteristics of the current frequency carrying the circulating current component in the bridge arm current based on the phase sequence characteristics of the three-phase bridge arm current frequency. The acquisition module is used to obtain the current frequency of the circulating current component based on the phase sequence characteristics of the current frequency of the circulating current component; the current frequency of the circulating current component is the circulating frequency that is not a single frequency multiple of the power frequency and the low frequency. The processing module is used to continuously iterate and eliminate the circulating current frequency by performing Park changes on the three-phase bridge arm current with a rotation angle of low frequency and twice the low frequency, then adjusting it with PR controllers with resonant frequencies of power frequency and twice the power frequency, and finally synthesizing the bridge arm circulating current component after modulation coefficient and inverse Park changes.

[0087] Compared with the prior art, the present invention has the following beneficial effects: The circulating current component, which interferes with the stability of the modular multilevel matrix converter (MMC), is decoupled. The phase sequence characteristics of the three-phase arm current frequencies are analyzed to determine the phase sequence characteristics of the current frequency carrying the circulating current component. Based on these phase sequence characteristics, the circulating current frequency is obtained, which is a non-single frequency multiple of the power frequency and a low-frequency frequency. The power frequency and low-frequency frequency of the circulating current component are obtained. After Park variation of the three-phase arm current with rotation angles of the low-frequency and twice the low-frequency, the current is adjusted by PR controllers with resonant frequencies of the power frequency and twice the power frequency, respectively. After modulation coefficient and inverse Park variation, the circulating current component is synthesized in the modulation signal, and the circulating current frequency is iteratively eliminated. Therefore, the method of this invention can suppress the circulating current component from the circulating current of the modular multilevel matrix converter, thereby improving the stability of the MMC.

[0088] Example 2 like Figure 12 As shown, the present invention also provides an electronic device 100 for implementing a circulating current control method for a positive and negative sequence PR modular multilevel matrix converter; The electronic device 100 includes a memory 101, at least one processor 102, a computer program 103 stored in the memory 101 and executable on at least one processor 102, and at least one communication bus 104.

[0089] The memory 101 can be used to store the computer program 103. The processor 102 implements the steps in the positive and negative sequence PR modular multilevel matrix converter circulating current control method of Embodiment 1 by running or executing the computer program stored in the memory 101 and calling the data stored in the memory 101.

[0090] The memory 101 may primarily include a program storage area and a data storage area. The program storage area may store the operating system, application programs required for at least one function (such as sound playback function, image playback function, etc.), etc.; the data storage area may store data created based on the use of the electronic device 100 (such as audio data), etc. In addition, the memory 101 may include non-volatile memory, such as hard disk, RAM, plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, at least one disk storage device, flash memory device, or other non-volatile solid-state storage device.

[0091] At least one processor 102 may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. Processor 102 may be a microprocessor or any conventional processor. Processor 102 is the control center of electronic device 100, connecting various parts of electronic device 100 via various interfaces and lines.

[0092] The memory 101 in the electronic device 100 stores multiple instructions to implement a positive-negative sequence PR modular multilevel matrix converter circulating current control method, and the processor 102 can execute multiple instructions to achieve the following: Decouple the circulating current component from the valve-side current of the M3C power frequency transformer, the valve-side current of the low frequency transformer, and the bridge arm current. The phase sequence characteristics of the current frequency carrying the circulating current component in the bridge arm current are analyzed based on the phase sequence characteristics of the three-phase bridge arm current frequency. The circulating current frequency is obtained based on the phase sequence characteristics of the circulating current frequency; the circulating current frequency is a non-single frequency multiple of the power frequency and the low frequency. After the three-phase bridge arm current is varied by Park with a rotation angle of low frequency and twice the low frequency, it is adjusted by PR controller with a resonant frequency of power frequency and twice the power frequency, and then the bridge arm circulating current component is synthesized by modulation coefficient and inverse Park variation to continuously eliminate the circulating current frequency.

[0093] Example 3 If the modules / units integrated in the electronic device 100 are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, and read-only memory (ROM).

[0094] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0095] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0096] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0097] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0098] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A circulating current control method for a positive and negative sequence PR modular multilevel matrix converter, characterized in that, include: Decouple the circulating current component from the valve-side current of the M3C power frequency transformer, the valve-side current of the low frequency transformer, and the bridge arm current. The phase sequence characteristics of the current frequency carrying the circulating current component in the bridge arm current are analyzed based on the phase sequence characteristics of the three-phase bridge arm current frequency. The circulating current frequency is obtained based on the phase sequence characteristics of the circulating current frequency; the circulating current frequency is the circulating frequency that is a non-single frequency multiple of the power frequency and the low frequency. After the three-phase bridge arm current is varied by Park with a rotation angle of low frequency and twice the low frequency, it is adjusted by PR controller with a resonant frequency of power frequency and twice the power frequency, and then the bridge arm circulating current component is synthesized by modulation coefficient and inverse Park variation to continuously eliminate the circulating current frequency.

2. The circulating current control method for a positive and negative sequence PR modular multilevel matrix converter according to claim 1, characterized in that, The step of iteratively eliminating the circulating current frequency by performing Park changes on the three-phase bridge arm current with rotation angles of low frequency and twice the low frequency, adjusting it with PR controllers with resonant frequencies of power frequency and twice the power frequency respectively, and then synthesizing the bridge arm circulating current component after modulation coefficient and inverse Park changes, specifically includes: The three-phase bridge arm current is first changed by Park and then passes through a PR controller. The PR controller has a resonant bandwidth of twice the power frequency, and then passes through a modulation coefficient. and synchronous rotating reference angle at low frequency The first inverse Park transform yields the first circulating modulated signal component. The first Park change uses a low-frequency frequency as the synchronous rotation reference angle. The three-phase bridge arm current is transformed by a second Park change and then passed through a PR controller, which uses the power frequency as its resonant bandwidth, and then modulated by a modulation coefficient. And rotate the reference angle synchronously at twice the low frequency. The second inverse Park transform yields the second circulating modulated signal component. The second Park change uses a synchronous rotation parameter at twice the low frequency as the rotation angle. First circulating modulation signal component Second circulating modulation signal component The combined components are the bridge arm circulation components.

3. The circulating current control method for a positive and negative sequence PR modular multilevel matrix converter according to claim 2, characterized in that, The three-phase bridge arm current is first changed by Park and then passes through a PR controller. The PR controller has a resonant bandwidth of twice the power frequency, and then passes through a modulation coefficient. and synchronous rotating reference angle at low frequency The first inverse Park transform yields the first circulating modulated signal component. ,include: The three-phase bridge arm current , and The first d-axis current component and the first q-axis current component are generated by the synchronous rotating reference angle at a low frequency after the first Park change. Obtain the d-axis and q-axis reference values ​​of the bridge arm circulating current, and obtain the difference of the first d-axis circulating current by subtracting the d-axis reference value of the bridge arm circulating current from the first d-axis current component. The difference between the bridge arm circulating current q-axis reference value and the first q-axis current component is used to obtain the difference in the first q-axis circulating current. ; The difference of the first d-axis circulation Difference from the first q-axis circulation As a PR controller The input signal of the PR controller The resonant bandwidth is twice the power frequency, modulated by the coefficient. and synchronous rotating reference angle at low frequency The first inverse Park transform yields the first circulating modulated signal component. .

4. The circulating current control method for a positive and negative sequence PR modular multilevel matrix converter according to claim 2, characterized in that, The three-phase bridge arm current is transformed by a second Park change and then passed through a PR controller, which uses the power frequency as its resonant bandwidth, and then modulated by a modulation coefficient. And rotate the reference angle synchronously at twice the low frequency. The second inverse Park transform yields the second circulating modulated signal component. ,include: The three-phase bridge arm current , and The second d-axis current component and the second q-axis current component are generated by a synchronous rotating reference angle at twice the low frequency through a second Park change. The difference between the bridge arm circulating current d-axis reference value and the current component of the second d-axis is used to obtain the difference in the second d-axis circulating current. The difference between the bridge arm circulating current q-axis reference value and the second q-axis current component is used to obtain the difference in the second q-axis circulating current. ; The difference between the second d-axis circulation Difference between the second q-axis circulation As a PR controller The input signal, The resonant bandwidth is the power frequency, modulated by the coefficient. and a synchronous rotating reference angle at twice the low frequency The second inverse Park transform yields the second circulating modulated signal component. .

5. The circulating current control method for a positive and negative sequence PR modular multilevel matrix converter according to claim 1, characterized in that, Based on the phase sequence characteristics of the three-phase bridge arm current frequency, the phase sequence characteristics of the current frequency carrying the circulating current component in the bridge arm current are analyzed, including: Based on Kirchhoff's current theorem, the relationship between the bridge arm current, the valve-side current of the M3C power frequency transformer, and the valve-side current of the low frequency transformer is obtained, and the time-domain expression of the bridge arm capacitor voltage is obtained. The time-domain expression of the bridge arm voltage is obtained from the time-domain expression of the bridge arm capacitor voltage; The time-domain expression of the bridge arm voltage is expanded to obtain the bridge arm capacitor voltage frequency. The bridge arm current frequency is then derived from the bridge arm capacitor voltage frequency, and the phase sequence characteristics of the bridge arm current frequency are determined. Based on the phase sequence characteristics of the bridge arm current frequency, the phase sequence characteristics of the bridge arm current frequency are subjected to modulo operation, and the modulo-processed value is taken as... The current components of the bridge arms are extracted to obtain the circulating current components, and the current frequency and phase sequence characteristics of the circulating current components are determined.

6. The circulating current control method for a positive and negative sequence PR modular multilevel matrix converter according to claim 1, characterized in that, The specific steps for decoupling the circulating current component from the valve-side current of the M3C power frequency transformer, the valve-side current of the low frequency transformer, and the arm current include: Based on Kirchhoff's current law, the relationship between the valve-side current of the M3C power frequency transformer, the valve-side current of the low frequency transformer, and the bridge arm current is obtained. Based on the relationship between the valve-side current of the M3C power frequency transformer, the valve-side current of the low frequency transformer, and the bridge arm current, the time-domain expressions of the M3C power frequency loop, the low frequency loop, and the circulating current loop are obtained. The time-domain expression of the circulating current loop includes the circulating current component, the M3C power frequency component, and the low frequency component. The time-domain expression of the circulating loop is decoupled to obtain the circulating component.

7. The circulating current control method for a positive and negative sequence PR modular multilevel matrix converter according to claim 6, characterized in that, The specific steps to decouple the time-domain expression of the circulating loop and obtain the circulating components include: Calculate the differential mode voltage of the M3C bridge arm. : in, It is the bridge arm voltage. This refers to the common-mode voltage of the M3C power frequency bridge arm. It is the low-frequency bridge arm common-mode voltage; Will Substituting into the time-domain expression of the circulating current loop, where the time-domain expression of the circulating current loop is: in, It is the bridge arm resistance. It is the circulating component. , This is the equivalent neutral point voltage; The circulating component is decoupled after transforming the time-domain expression of the circulating loop. .

8. A circulating current control device for a positive and negative sequence PR modular multilevel matrix converter, characterized in that, include: The decoupling module is used to decouple the circulating current component from the valve-side current of the M3C power frequency transformer, the valve-side current of the low frequency transformer, and the bridge arm current. The analysis module is used to analyze the phase sequence characteristics of the current frequency carrying the circulating current component in the bridge arm current based on the phase sequence characteristics of the three-phase bridge arm current frequency. The acquisition module is used to obtain the current frequency of the circulating current component based on the phase sequence characteristics of the current frequency of the circulating current component; the current frequency of the circulating current component is the circulating frequency that is not a single frequency multiple of the power frequency and the low frequency. The processing module is used to continuously iterate and eliminate the circulating current frequency by performing Park changes on the three-phase bridge arm current with a rotation angle of low frequency and twice the low frequency, then adjusting it with PR controllers with resonant frequencies of power frequency and twice the power frequency, and finally synthesizing the bridge arm circulating current component after modulation coefficient and inverse Park changes.

9. An electronic device, characterized in that, It includes a processor and a memory, the processor being used to execute a computer program stored in the memory to implement a positive and negative sequence PR modular multilevel matrix converter circulating current control method as described in any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores at least one instruction, which, when executed by a processor, implements a positive-negative sequence PR modular multilevel matrix converter circulating current control method as described in any one of claims 1 to 7.

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